Web tension control apparatus for use with a rotary press

ABSTRACT

The web tension control apparatus according to the present invention is provided with a biasing roller (6) adapted to be urged against the outer circumferential surface of a midway drag roller (4), a biasing means (7) adapted to apply an urging force in the biasing direction against the biasing roller (6) for the midway drag roller, a tension detecting means (7), (9) adapted to detect the tension of a running web (1) upstream and downstream of a printing unit (2), and a control means (10) adapted to control the urging force of the biasing device 7 in accordance with the signals from the tension detecting means (7), (9). If there is any difference in the signals from the tension detecting means (7), (9), the control device (10) controls the biasing roller (6) for the midway drag roller (4) by the aid of the biasing device (7) so as to eradicate the difference in the signals, so that the tensions web upstream and downstream of the printing unit (2) are equal with each other. Any losses of the tension in the web (1) as generated in the slotted section of a printing cylinder may be prevented from occurring, and any variations in the tensions of the web (1) may be relieved substantially so that defects in the printing such as the offset doubles and the deviations in cutting the printings, etc. may be obviated accordingly.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for controlling thetension of a running print sheet or web for use with a rotary press.

2. Description of the Related Art

A typical monochromatic perfecting unit and of a typical monochromaticperfecting and multicolor oneside printing unit for use with aconventional rotary press are shown in FIG. 1 and FIG. 2, respectively.According to the monochromatic perfecting unit as shown in FIG. 1, arunning printing sheet or web of paper 1 is, after having been printedby the monochromatic perfecting unit 2, directed through a guide roller3 toward a midway drag roller 4, whereby the web of paper is subjectedto traction to be delivered to following operations.

According to the monochromatic perfecting unit and the multicolor oneside printing unit as typically shown in FIG. 2, the running web 1 is,after having been printed by the monochromatic perfecting unit 2,directed through a guide roller 5 toward a midway drag roller 4, wherebythe web is subjected to traction to be delivered to a multicolor oneside printing unit 5, where the web is subjected to the multicolorprinting operations and is then redirected to following procedures inthe printing line.

In the construction of the rotary press as schematically shown in FIGS.1 and 2, it is observed that there occurs a substantial variation intension of the running web 1 extending in the upstream and downstream ofthe monochromatic perfecting unit 2 and the multicolor one-side printingunit 5. This variation in tension of the web is considered to resultfrom the possible loss of tension by way of the slots of the printingcylinder and of vibrations occurring per one operating cycle of theprinting cylinder, and such variations in tension result in such faultssuch as deviations in the cutting of the printings and such as offsetdoubles, or the like.

SUMMARY OF THE INVENTION

In consideration of such problems as noted above, it is an object of thepresent invention to provide a tension control apparatus for use with arotary press which can prevent the faults in the conventional printingunits such as the occurrence of offset doubles and the deviation in thecutting of the printings, by eliminating possible variations in thetension of a running printing sheet or web upstream and downstream ofthe printing units incorporated in the rotary press line.

According to the invention, there is provided a tension controlapparatus for use with a rotary press, which comprises, as brieflysummarized, a midway drag biasing roller adapted to be urged resilientlyagainst the outer circumferential surface of a midway drag roller, abiasing device adapted to resiliently apply an urging pressure upon themidway drag biasing roller so that it may be urged properly in thebiasing direction, a tension detecting device adapted to detect thetensions of the printing sheet or web extending upstream and downstreamof a printing unit, and a control device adapted to control the urgingforce of the biasing device in accordance with due signals from thetension detecting device, so that the tensions of the running webupstream and downstream of the printing unit may be equalized, wherebythere is attained such advantageous effects such as preventing a loss oftension in the printing web as would be encountered in the area of theslotted section of a printing cylinder, and such as reducing possiblevariations in the tension of the running web, thus resulting in theefficient prevention of defects such as offset doubles and variations inthe cutting of the printings.

The present invention will now be described by way of preferredembodiments thereof taken with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 and 2 are schematic views show portions of conventional printingunits;

FIG. 3 is a schematic view showing the system of a tension controlapparatus by way of a preferred embodiment of the present invention foruse with a rotary press;

FIG. 4 is a schematic view showing the system by way of anotherembodiment of the present invention;

FIG. 5 is a schematic side elevation view showing a preferred embodimentof a midway drag roller of the present invention; and

FIG. 6 is an enlarged front elevation view showing the midway dragroller of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

A tension control apparatus according to the present invention for usewith a rotary press shown in FIG. 3 is now described by way of apreferred embodiment, which is shown comprising a running sheet or webof printing paper designated at the reference numeral 1, a monochromaticperfecting unit at 2, a guide roller at 3, a midway drag roller at 4, abiasing roller at 6 which is not rotatably driven resiliently urgedtoward the midway drag roller 4, and a biasing device at 7 for causingthe biasing roller 6 to be biased under a biasing force against themidway drag roller 6. Also, a tension detector 8 is provided in theguide roller 3, and a floating or dancer roller 9 is provided upstreamof the monochromatic perfecting unit 2. The detection of the tension inthe running web 1 passing through the monochromatic perfecting unit 2and the guide roller 3 is conducted in such a manner that a signalrepresenting the tension detected as a load rendered by the dancerroller 9 upstream of the monochromatic perfecting unit 2 and a signalrepresenting the tension as detected by the tension detector 8 are fedto a control unit 10 which is adapted to control the biasing device 7.

Now, referring to the operation of the web tension control apparatus foruse with the rotary press shown in FIG. 3, the running web of printingpaper 1 is directed to extend toward to the monochromatic perfectingunit 2, the web 1 being tensioned upstream of the unit 2, and thereafterfed into the unit 2 for printing. After printing, the running web 1 isthen directed to pass through the guide roller 3, where the tension ofthe web 1 on the delivery side of the monochromatic perfecting unit 2 isdetected by the tension detector 8 which is provided in the guide roller3, and then is sent out to the midway drag roller 4. It is arranged sothat the outer circumferential speed of the midway drag roller 4 is setto be 1% greater than that of the monochromatic perfecting unit 2, andthat the midway drag roller 4 slips with respect to the web 1 to anextent of a difference in the speeds of the two. With this arrangement,the midway drag roller 4 may render a dragging or friction force whichis generally proportional to the biasing force of the biasing roller 6upon the web 1, so that the tension of the web 1 may be controlledexclusively in accordance with the biasing force from the biasing roller6, accordingly.

If the tension signal which is detected by the dancer roller 9, forexample a voltage signal, and the tension signal as detected by thetension detector 8, for example a voltage signal, are each proportionalto the detected tension of the web 1, and these signals are fed into thecontrol device 10, where they are compared with each other for anydifference in magnitide of voltage, and if any, the control device 10functions to generate a control signal which compensates for thedifference in these signals, the control signal of the control device 10is delivered to the biasing device 7 so that the biasing roller 6 mayrender an appropriate biasing force upon the midway drag roller 4 so asto control the tension of the web 1 accordingly. For instance, if thecurrent tension as detected in the web 1 after passing the monochromaticperfecting unit 2 is found smaller than that upstream of the unit 2, thebiasing device 7 is operated to urge the biasing roller 6 so as toincrease the tension in the web 1, and vice versa. With such a tensioncontrol operation, the tensions present in the web 1 before and afterpassing through the monochromatic perfecting unit 2 are efficientlyregulated to be equal to each other. Once the difference in the tensionsin the web 1 across the monochromatic perfecting unit 2 is eliminated,there is no longer a chance of tension losses at the slotted section ofthe print cylinder, thus relieving possible variations in the tension ofthe web 1 and thus preventing defects such as the offset doubles, anddeviations in cutting the printings, etc. from occurring.

FIG. 4 shows another embodiment of the invention which is adapted to therotary press employing the monochromatic perfecting unit 2 and themulticolor one-side printing unit 5 shown in FIG. 2.

According to the construction of the multicolor one-side printing unit 5shown in FIG. 4, a plurality of sets of blanket cylinders 12 are urgedtoward the outer circumference of an impression cylinder 11. With suchan arrangement, should a loss of tension in the web 1 by the slottedsection in the printing cylinder occur while the web is held and fed ina sandwiched relationship between the impression cylinder 11 and theblanket cylinders 12, since some sets of blanket cylinders 12 may stillserve to efficiently hold the web 1 in position around the circumferenceof the impression cylinder 11, only relatively small tension lossesoccur from the slotted section in the printing cylinder, thusefficiently preventing such faults in the printing from occurring asaccomplished with the advantageous construction shown in FIG. 3,accordingly.

Next, referring to a preferred embodiment of the midway drag roller 4shown in FIGS. 5 and 6, a running web of printing paper 1, a midway dragroller 4 having a flat portion 4a with a flat circumferential surfaceand a groove portion 4b formed with a plurality of grooves extendingparallel to each other and disposed in alternate fashion with the flatportion, and a biasing roller 6 adapted to urge the web 1 upon the flatportions 4a of the midway drag roller 4 are provided.

Now, the operation of the midway drag roller 4 as shown in FIGS. 5 and 6will be described. It is seen that the web 1 is urged against the outercircumferential surface of the midway drag roller 4 by the biasingroller 6 while passing therethrough, with an appropriate tension valueto following operations. At this stage, the web 1 would possibly proceedin zigzag manner with a too large of a tension rendered, which wouldresult in a breakage of and wrinkle in the web 1. In this respect, it isrequired to maintain an appropriate tension within an optimal range.According to this embodiment, by virtue of such a unique construction ofthe midway drag roller 4 which is provided the flat portions 4a and thegrooved portions 4b disposed in an alternate manner so that there areformed a plurality of grooves extending in parallel and in thecircumferential direction in the outer circumferential surface of theroller 4, there is attained such an advantageous effect that the groovedportions 4b in the roller surface may let air entrapped by the web 1escape, thus preventing the loss of frictional drive force from thecircumferential surface of the midway drag roller 4 from occurring andthus, the biasing roller 6 serves to effiently urge the web 1 upon theflat portions 4a thereof so that the tension of the web 1 may becontrolled optimally. Incidentally, it is empirically known that whenthe outer circumference of the midway drag roller 4 is made partly flat,the coefficient of friction is reduced merely from a few percent totenths of a percent in comparison with a drag roller which is providedwith a plurality of grooves in the entire circumferential area ofthereof.

As reviewed fully hereinbefore, with the improved construction such thatthe midway drag roller 4 is designed with its outer circumferentialsurface comprising the plurality of flat portions 4a sandwiched betweenthe adjacent grooved portions 4b extending parallel to one another inthe circumferential direction, and the biasing roller 6 is urged towardthe flat portions 4a of the midway drag roller 4 so that the biasingroller 6 may serve to urge the flat portions 4a of the midway dragroller 4 through the running web 1 sandwiched therebetween, there is nopossibility that the grooves will leave any undesired marks orimpressions on the surface of the web 1 even with a substantial urgingforce rendered thereupon, thus making it feasible in practice to have asubstantially widened range of tension control for the running web 1 incomparison with the conventional construction in which there are formeda plurality of grooves the entire outer circumferential area of the dragroller 4. Also, it provides another advantageous feature in that therunning web 1 may be held in an optimal condition while being fed alongthe printing line because it ensures that the web 1 is free from anymarks of grooves in the urging roller.

We claim:
 1. A web tension control apparatus for a rotary press having arotating printing unit through which the web passes, comprising:a midwaydrag roller downstream of the printing unit and over which the webtravels, and means for driving the midway drag roller so as to have acircumferential speed that is slightly higher than that of the rotatingprinting unit for causing the midway drag roller to slip with respect tothe web travelling thereover to an extent corresponding to thedifference in the circumferential speeds of the midway drag roller andthe printing unit; a biasing roller adjacent the outer circumferentialsurface of the midway drag roller at a location at which the web travelsover the midway drag roller, and a biasing means for applying an urgingforce in a biasing direction against said biasing roller for urging thebiasing roller toward the outer circumferential surface of the midwaydrag roller to press the web against said midway drag roller at saidlocation; a tension detecting means for detecting the tension of the webupstream of the printing unit, for detecting the tension of the webdownstream of the printing unit, and for issuing a signal indicative ofthe detected tensions; and a control means operatively connected betweensaid biasing means and said tension detecting means for receiving thesignal from said tension detecting means and for controlling the urgingforce imparted by said biasing means to the biasing roller in accordancewith the signal received.
 2. An apparatus as claimed in claim 1,whereinsaid midway drag roller comprises a plurality of flat portions andgrooved portions alternately disposed around the outer circumferentialsurface, the grooved portions each having a plurality of groovesextending parallel to one another, and said biasing means is for urgingthe biasing roller toward the outer circumferential surface of themidway drag roller to press the web against the flat portions of themidway drag roller.
 3. An apparatus as claimed in claim 1,wherein saidcontrol means controls the urging force imparted by said biasing meansfor regulating the tension of the web downstream of the printing unit toa predetermined value in comparison with tension of the web upstream ofthe printing unit as detected by said tension detecting means.